The present invention is directed to a linerless, threaded, molded plastic closure, particularly intended for use with glass bottles containing pressurized liquids, but also suitable for use with other types of containers and for non-pressurized applications.
The carbonated-beverage industry produces large amounts of a bulky product in which the container package must meet severe performance requirements while representing a relatively large percentage of the total product cost. Under these conditions, the need for a container closure which is highly efficient and at the same time economical is evident.
In addition to the primary need for a closure which will provide for the retention of high gas pressures in combination with low installed cost, there are numerous secondary needs, some of which are nearly as important. These may be subdivided among those relating to manufacture, distribution, and use of the product, as described below.
During manufacture of the product it is desirable to be able to use closures which will operate with typical industry-standardized bottle-top finishes, without requiring the provision of unusual or proprietary bottle constructions. This facilitates the use of existing equipment, and the re-use of bottles to prevent littering. It is also desirable to be able to use standard bottling equipment with a minimum of special tools, processes and maintenance, and under circumstances which provide favorable sanitary conditions.
During distribution, the closure must be able to withstand repeated handlings, with their associated impacts and abrasions. Storage also presents particular problems, since the product must maintain a high percentage of the original gas pressure over a period of several weeks or months. Many of the storage problems are related to temperature conditions, which may range from near-freezing during refrigeration, or during winter storage, to high temperatures in some warehouses in hot areas. However, some are related to less obvious storage conditions, as when several open-top cases of the bottled product are stacked, so that the entire weight of the stack may rest on a few of the closures and containers of the bottom case.
In customer use, it is desirable to have the closure readily removable by a person of less than average strength, without the use of a special uncapping tool. It should have effective means for assuring the user that the bottle has not previously been opened. It should be relatively free from any tendency to blow off prematurely during unscrewing of the closure. It should be resealable after the initial opening, so that any of the product not used immediately can be conserved for future use with minimum loss of pressure. Finally, it should be reclaimable, so that, where conditions of use permit, the used closures can be reprocessed and the material re-used, in order to conserve material and prevent littering.
In the past, closures for pressurized applications have usually been made of metal with a resilient cork or plastic liner. The metal closures have been acceptable from the production and distribution standpoints, but have had shortcomings from the viewpoint of the user. Those which do not require a special tool for removal are likely to require relatively strong fingers, and may tend to cut the fingers. If effective tamper-indicating means are provided, it is usually in the form of a retained metal ring around the neck which deters re-use of the bottle and/or recycling of the material. Resealability is impracticable with non-threaded metal closures, and is not always reliable with threaded ones on account of the irregular thread friction often encountered when they are used with glass bottles. Finally, reclaimability of the closure material is limited because of the combination of metal and sealing material.
Linerless, threaded, molded plastic closures are an attractive alternative to the metal-based closures, since they are potentially free of the user-related limitations cited above. However, they have not yet been able to meet adequately some of the distribution requirements mentioned, especially those involving pressure-retention and top-loading during extended storage. The problems in these areas are particularly evident when using such closures in combination with glass bottles, which have much larger variations in dimensional accuracy and surface finish than the corresponding plastic or metal containers. For this reason, a closure which is acceptable for use with the latter may not be satisfactory for glass.
It is therefore clear that a need exists for a plastic closure which is particularly adapted to the special conditions associated with glass bottles as widely used in the carbonated-beverage industry, and which will provide a combination of features enabling it to meet, in an acceptable degree, all of the specific needs of this application. Such a closure should, at the same time, be suitable for many less-demanding applications.